1. Field of the Invention
The invention relates to a high pressure piston pump and more particularly, to a piston pump especially useful for high pressure delivery of fuel in fuel injection systems of internal combustion engines.
2. Description of the Prior Art
A piston pump of this kind has been disclosed in (DE 44 01 074 A1). In this known pump, a first plate is embodied in the shape of a flange with a central cylinder, which has a pump piston and is aligned radially in relation to a drive shaft of the pump, and approximately half of its plate thickness is contained in a countersink of a pump housing. A valve plate is supported on the side of the first plate oriented away from the shaft and has a first and a second check valve. The first plate and the valve plate are covered by a second plate that closes off the pump housing and is screwed to the pump housing. The second plate contains a conduit that carries low-pressure fuel and communicates at one end with a conduit of the pump housing and communicates at the other end with the first check valve. Between the pump housing and the second plate, a rubber elastic shaped seal, which encloses both the conduit and the flange-shaped first plate, is contained in a recess of the second plate. A second conduit, which leads from the second check valve and carries high-pressure fuel, transitions from the second plate into the pump housing by means of a connecting piece. The connecting piece is embodied as socket-shaped and engages in both the second plate and the pump housing. The connecting piece is sealed in relation to the second plate and the pump housing by means of annular, rubber elastic high-pressure seals.
In the known radial piston pump, the second plate is represented as resting completely against the pump housing. In actual use, however, a gap of a few tenths of a millimeter must be provided between the plate and the pump housing in order to compensate for tolerances of the interconnected componentsxe2x80x94the pump housing, first plate, valve plate, and second platexe2x80x94as well as to produce a play-free and fuel-tight placement of the first plate against the pump housing and of the valve plate between the first plate and the second plate.
Because of this design of the radial piston pump, assembly errors can occur which can impair the pump function or can cause the pump to fail. For example, potential errors include incorrect insertion of the shaped seal into the recess in the second plate resulting in a cross sectional reduction of the first conduit, tilting of the connecting piece in the course of the second conduit resulting in a leak as well as a skewed positioning of the second plate, wherein the latter error can also be caused by uneven screwing of the second plate to the pump housing.
The piston pump according to the invention, has the advantages over the prior art that fewer structural components are used than in the known prior art, that a definite geometrical association of the two plates that rest flat against each other is achieved, and that the second check valve is disposed in a favorable position from a production and assembly engineering standpoint.
In addition, seals are used which are advantageously adapted with regard to sealing in a manner consistent with the installation location and the load.